A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that instance, a patterning device, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g., comprising part of, one, or several dies) on a substrate (e.g., a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned.
Lithography is widely recognized as one of the key steps in the manufacture of ICs and other devices and/or structures. However, as the dimensions of features made using lithography become smaller, lithography is becoming a more critical factor for enabling miniature IC or other devices and/or structures to be manufactured.
A theoretical estimate of the limits of pattern printing can be given by the Rayleigh criterion for resolution as shown in equation (1):
                    CD        =                              k            1                    *                      λ            NA                                              (        1        )            where λ is the wavelength of the radiation used, NA is the numerical aperture of the projection system used to print the pattern, k1 is a process dependent adjustment factor, also called the Rayleigh constant, and CD is the feature size (or critical dimension) of the printed feature. It follows from equation (1) that reduction of the minimum printable size of features can be obtained in three ways: by shortening the exposure wavelength λ, by increasing the numerical aperture NA or by decreasing the value of k1.
In order to shorten the exposure wavelength and, thus, reduce the minimum printable size, it has been proposed to use an extreme ultraviolet (EUV) radiation source. EUV radiation is electromagnetic radiation having a wavelength within the range of 10-20 nm, for example within the range of 13-14 nm. It has further been proposed that EUV radiation with a wavelength of less than 10 nm could be used, for example within the range of 5-10 nm such as 6.7 nm or 6.8 nm. Such radiation is termed extreme ultraviolet radiation or soft x-ray radiation. Possible sources include, for example, laser-produced plasma sources, discharge plasma sources, or sources based on synchrotron radiation provided by an electron storage ring.
EUV radiation may be produced using a plasma. A radiation system for producing EUV radiation may include a laser for exciting a fuel to provide the plasma, and a source collector module for containing the plasma. The plasma may be created, for example, by directing a laser beam at a fuel, such as particles of a suitable material (e.g., tin), or a stream of a suitable gas or vapor, such as Xe gas or Li vapor. The resulting plasma emits output radiation, e.g., EUV radiation, which is collected using a radiation collector. The radiation collector may be a mirrored normal incidence radiation collector, which receives the radiation and focuses the radiation into a beam. The source collector module may include an enclosing structure or chamber arranged to provide a vacuum environment to support the plasma. Such a radiation system is typically termed a laser produced plasma (LPP) source.
A chuck may be provided for holding a patterning device for imparting a radiation beam with a pattern in its cross section or a substrate for receiving the patterned radiation beam. The chuck may be configured to hold the patterning device or substrate by electrostatic attraction. The chuck may provide Johnsen-Rahbek (JR) clamping, Coulomb clamping, or both, for example. The temperature of the chuck may be controlled by driving a temperature conditioning fluid through channels formed within the chuck. It has been found in such arrangements that the interior walls of the channels, and/or of apparatus external to the chuck that is in contact with the fluid, can degrade over time.
It has also been found that electric current formed within the chuck during operation can lead to resistive heating of the chuck. Such heating can be compensated by the fluid in the channels. However, it can be difficult to compensate for sudden changes in the dissipated power, for example when the chuck is turned off to unmount a patterning device or substrate.
US 2009/207392 A discloses a lithographic apparatus configured to transfer a pattern from a patterning structure, held by a patterning structure holder, onto a substrate that is held by a substrate holder. The apparatus includes a first object holder configured to hold an object, and an object temperature conditioner configured to condition a temperature of the object prior to and/or during transfer of the objection to the first object holder. The object temperature conditioner includes a second object holder having a fluid duct system and an electrical temperature conditioner.
WO 92/20093 A discloses an electrostatic chuck assembly including a top multilayer ceramic insulating layer, and electrostatic pattern layer having a conductive electrostatic pattern disposed on a multilayer ceramic substrate, a multilayer ceramic support layer, and, a heat sink base having back side cooling channels machined therein. The heat sink base is brazed to the bottom of the multilayer ceramic support layer.